EP 722 850 B1 discloses a low-permeability thermoplastic elastomer composition that is superior as a gas-barrier layer in pneumatic tires. This thermoplastic elastomer composition comprises a low-permeability thermoplastic matrix, such as polyamide or a blend of polyamides, in which there is dispersed a low-permeability rubber, such as brominated poly(isobutylene-co-paramethylstyrene), typically referred to as BIMS. In EP 857 761 A1 and EP 969 039 A1, the viscosity ratio of the thermoplastic matrix and the dispersed rubber phase was specified both as a function of the volume fraction ratio and, independently, to be close to a value of one in order to produce a high concentration of small particle size vulcanized rubber particles dispersed in a thermoplastic phase. EP 969 039 A1 further discloses that small particle size rubber dispersed in a thermoplastic resin matrix was useful in order to achieve acceptable durability of the resulting composition, particularly where such compositions are intended to be used as innerliners in pneumatic tires. Further improvements in the technology for producing thermoplastic elastomer compositions useful for industrial applications are described by the inventors herein and others in US Published Applications 2006/0223941 and 2007/0060684, incorporated herein by reference.
Compositions exhibiting low gas permeability performance (i.e., functioning as a gas barrier) composed of thermoplastic resin/thermoplastic resin-based blends such as a high density polyethylene resin and nylon 6 or nylon 66 (HDPE/PA6/PA66), a polyethylene terephthalate and aromatic nylon (PET/MXD6), a polyethylene terephthalate and vinyl alcohol-ethylene copolymer (PET/EVOH), where one thermoplastic resin is layered over the other layer to form plural layers by molding, and processes for producing the same, are disclosed. Further, an application regarding the use of such a composition as the innerliner layer of a tire is disclosed in Japanese Patent Application No. 7-55929 (i.e., JP-A-7-55929). However, since these materials are thermoplastic resin/thermoplastic resin blends, while they are superior in gas barrier performance, they lack flexibility, and therefore, such films are subject to failure if they are used in a vehicle tire which is subject to significant stress and flexing.
Further, there are also examples of the use of a thermoplastic elastomer composed of a rubber and a thermoplastic resin for use as an innerliner or in a tire; see, Japanese Patent Application No. 8-183683 (i.e., JP-A-8-183683), but in general, a flexible material of the type disclosed therein and having superior durability has low heat resistance. With a thermoplastic elastomer using a thermoplastic resin having a melting point less than the tire vulcanization temperature as a matrix, when the tire vulcanization bladder is released at the end of the tire vulcanization cycle, the tire inside surface is subject to appearance defects due to the thermoplastic resin sticking to or rubbing against the vulcanization bladder.
Control of the viscosity difference between the rubber and resin during mixing in order to reduce the particle size of the dispersed rubber has been reported by S. Wu, Polym. Eng. Sci., 27(5), 1987. Wu reported that the dispersed rubber particle size was reduced where the ratio of melt viscosities of the rubber/resin is brought close to 1, that is, when their viscosities are equal. However, it is reported in EP 969 039 A1 that, in attempting to fabricate a thermoplastic elastomer composition having sufficient flexibility, strength and elongation, as well as superior durability, by increasing the rubber content, and keeping the ratio of melt viscosities of the rubber/resin at 1, the rubber becomes the continuous matrix and such compositions containing vulcanized rubber no longer exhibit thermoplasticity.
In Japanese Patent Application Nos. 8-193545, 9-175150, and 10-235386 (i.e., JP-A-8-193545, JP-A-9-175150, and JP-A-10-235386, respectively), it is proposed that, in a laminate structure in which dynamic fatigue resistance is required, such as in a tire or a hose, when using a gas permeation preventive thermoplastic elastomer composition composed of rubber/resin dispersed therein, it is known to obtain a balance between the flexibility and gas permeation preventive property by making use of a blend of flexible N11- or N12-nylon and the superior gas permeation preventive property of N6- or N66-nylon. Further, it was proposed to define volume fraction and melt viscosity using the following equation, defined as alpha:(φd/φm)×(ηm/ηd)<1.0wherein the volume fractions of the continuous or matrix phase component and dispersed phase component in the thermoplastic elastomer composition are φm and φd respectively, and the melt viscosities of the matrix and dispersed phase components are ηm and ηd respectively, and further to bring the ratio of viscosities ηm/ηd close to 1 to reduce the dispersed rubber particle size domain in order to improve the durability. However, it is reported in EP 969 039 A1 that the durability at low temperatures was insufficient by just reducing the rubber particle size.
Thus the limitations of the prior approaches to achieving improved performance of the desirable compositions comprising a small particle size rubber domain dispersed in a thermoplastic matrix, the composition exhibiting improved gas or fluid barrier properties and desirable levels of strength and durability suitable for use in tires and hose applications suggest that there is a continuing need for improvements, as have been accomplished by use of the processes of the present invention.